SNDCTL_AUDIOINFO and SNDCTL_ENGINEINFO

A few days ago I stumbled into a bug report [1] which mentions that
FreeBSD's SNDCTL_AUDIOINFO and SNDCTL_ENGINEINFO do not exactly work
correctly. The problem is essentially that both IOCTLs return the same
information, while in fact the information returned currently by
dsp_oss_audioinfo() is what _only_ SNDCTL_ENGINEINFO is meant to return.

This behavior is also noted in the OSS manual [2] (see bold paragraph in
"Audio engines and device files" section), but I think that since the
DEVFS_CDEVPRIV(9) patch we can actually fix this, because we now expose
only a single device for each soundcard, and create the engines
(channels) internally. SNDCTL_ENGINEINFO will report info about all
channels in a given device (exactly what we do already), and
SNDCTL_AUDIOINFO will only report information about /dev/dspX.

The reason I writing this email however, is to hear your feedback on the
following. Both SNDCTL_AUDIOINFO and SNDCTL_ENGINEINFO expect the same
oss_audioinfo structure, so I am wondering what some of the fields will
be filled with for SNDCTL_AUDIOINFO.

Here are my thoughts about what we should fill the fields with:

dev		Device unit.
name		Either pcmX or device_get_desc(). I think the latter is
		better.
busy		Set this to true if we have >0 busy channels in the
		device?
pid		I think it's best to set this to -1. We could check if
		an application has exlusive access of the whole device,
		but I don't think this is useful in any way.
caps		We could gather the caps for every channel and OR them
		together, so we'll report all the currently enabled caps
		for the device.
iformats	Same as caps.
oformats	Same as caps.
cmd		Nothing. Same logic as pid.
card_number	Device unit.
song_name	Not supported.
label		Not supported.
port_number	Device unit.
mixer_dev	Device unit.
legacy_device	Device unit.
devnode		/dev/dspX
enabled		device_is_attached()
min_rate	Global (from all channels) minumum;
max_rate	Global maximum.
min_channels	Global minimum.
max_channels	Global maximum.
nrates, rates	Drivers do not support this yet, but I am not sure
		exactly what we should put here.
handle		Not supported.
next_play_engine	0
next_rec_engine		0

Christos

[1] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=246231
[2] http://manuals.opensound.com/developer/SNDCTL_AUDIOINFO.html